---
layout: docs
page_title: Seal/Unseal
sidebar_title: Seal/Unseal
description: >-
  A Vault must be unsealed before it can access its data. Likewise, it can be
  sealed to lock it down.
---

# Seal/Unseal

When a Vault server is started, it starts in a _sealed_ state. In this
state, Vault is configured to know where and how to access the physical
storage, but doesn't know how to decrypt any of it.

_Unsealing_ is the process of obtaining the plaintext master key necessary to
read the decryption key to decrypt the data, allowing access to the Vault.

Prior to unsealing, almost no operations are possible with Vault. For
example authentication, managing the mount tables, etc. are all not possible.
The only possible operations are to unseal the Vault and check the status
of the unseal.

## Why?

The data stored by Vault is stored encrypted. Vault needs the
_encryption key_ in order to decrypt the data. The encryption key is
also stored with the data (in the _keyring_), but encrypted with another
encryption key known as the _master key_.

Therefore, to decrypt the data, Vault must decrypt the encryption key
which requires the master key. Unsealing is the process of getting access to
this master key.  The master key is stored alongside all other Vault data,
but is encrypted by yet another mechanism: the unseal key.

To recap: most Vault data is encrypted using the encryption key in the keyring;
the keyring is encrypted by the master key; and the master key is encrypted by
the unseal key.

## Shamir seals

![Shamir](/img/vault-shamir-storage.png)

The default Vault config uses a Shamir seal. Instead of distributing the unseal
key as a single key to an operator, Vault uses an algorithm known as
[Shamir's Secret Sharing](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing)
to split the key into shards. A certain threshold of shards is required to
reconstruct the unseal key, which is then used to decrypt the master key.

This is the _unseal_ process: the shards are added one at a time (in any
order) until enough shards are present to reconstruct the key and
decrypt the master key.

## Unsealing

The unseal process is done by running `vault operator unseal` or via the API.
This process is stateful: each key can be entered via multiple mechanisms
on multiple computers and it will work. This allows each shard of the master
key to be on a distinct machine for better security.

Once a Vault node is unsealed, it remains unsealed until one of these things happens:

1. It is resealed via the API (see below).

2. The server is restarted.

3. Vault's storage layer encounters an unrecoverable error.

-> **Note:** Unsealing makes the process of automating a Vault install
difficult. Automated tools can easily install, configure, and start Vault,
but unsealing it using Shamir is a very manual process.  For most users
AutoUnseal will provide a better experience.

## Sealing

There is also an API to seal the Vault. This will throw away the master
key and require another unseal process to restore it. Sealing only requires
a single operator with root privileges.

This way, if there is a detected intrusion, the Vault data can be locked
quickly to try to minimize damages. It can't be accessed again without
access to the master key shards.

## Auto Unseal

Auto Unseal was developed to aid in reducing the operational complexity of
keeping the unseal key secure. This feature delegates the responsibility of
securing the unseal key from users to a trusted device or service.  At startup
Vault will connect to the device or service implementing the seal and ask it
to decrypt the master key Vault read from storage.

![AutoUnseal](/img/vault-autounseal-storage.png)

When using Auto Unseal there are certain operations in Vault that still
require a quorum of users to perform an operation such as generating a root token.
During the initialization process, a set of Shamir keys are generated that are called
_recovery keys_ and are used for these operations.

It is still possible to seal a Vault node using the API.  In this case Vault
will remain sealed until restarted, or the unseal API is used, which with AutoUnseal
requires the recovery key fragments instead of the unseal key fragments that
would be provided with Shamir.  The process remains the same.

For a list of examples and supported providers, please see the
[seal documentation](/docs/configuration/seal).

## Recovery Key Rekeying

During the KMS Seal initialization process, a set of Shamir keys called recovery keys are
generated which are used for operations that still require a quorum of users.

Recovery keys can be rekeyed to change the number of shares or thresholds. When using the
Vault CLI, this is performed by using the `-target=recovery` flag to `vault operator rekey`.

## Seal Migration

The seal can be migrated from Shamir Seal to KMS Seal, KMS Seal to Shamir Seal,
and KMS Seal to another KMS Seal.

~> **NOTE**: A backup should be taken before starting seal migration in case
something goes wrong.

~> **NOTE**: Seal migration process cannot be performed without downtime. Due to
the technical underpinnings of the seal implementations, it is at this point not
possible to perform seal migration without briefly bringing the whole cluster
down. We understand that it can be hard for many deployments to face downtime,
but we believe that switching seals is a rare event and hence we hope for the
downtime to be considered as an acceptable trade-off.

~> **NOTE**: Seal migration operation will require both old and new seals to be
available during the migration. For example, migration from KMS seal to Shamir
seal will require that the KMS key be accessible during the migration.

~> **NOTE**: Seal migration from KMS seal to KMS seal of same kind is not
currently supported. We plan to support this officially in a future release.

### Migration post Vault 1.5.1

These steps are common for seal migrations between any supported kinds and for
any storage backend.

1. Take a standby node down and update the [seal
   configuration](/docs/configuration/seal).

    * If the migration is from Shamir seal to KMS seal, add the desired new KMS
      seal block to the configuration.
    * If the migration is from KMS seal to Shamir seal, add `disabled = "true"`
      to the old seal block.
    * If the migration is from KMS seal to another KMS seal, add `disabled =
      "true"` to the old seal block and add the desired new KMS seal block.

    Now, bring the standby node back up and run the unseal command on each key, by
    supplying the `-migrate` flag.

    * Supply Shamir unseal keys if the old seal was Shamir, which will be migrated
      as the recovery keys for the KMS seal.
    * Supply recovery keys if the old seal is one of KMS seals, which will be
      migrated as the recovery keys of the new KMS seal, or as Shamir unseal
      keys if the new seal is Shamir.

1. Perform step 1 for all the standby nodes, one at a time. It is necessary to
   bring back the downed standby node before moving on to the other standby nodes,
   specifically when Integrated Storage is in use for it helps to retain the
   quorum.

1. [Step down](https://www.vaultproject.io/docs/commands/operator/step-down) the
   active node. One of the standby nodes will become the new active node.
   When using Integrated Storage, ensure that quorum is reached and a leader is
   elected.

1. The new active node will perform the migration. Monitor the server log in
   the active node to witness the completion of the seal migration process.
   Wait for a little while for the migration information to replicate to all the
   nodes in case of Integrated Storage. In enterprise Vault, switching a KMS seal
   implies that the seal wrapped storage entries get re-wrapped. Monitor the log
   and wait until this process is complete (look for `seal re-wrap completed`).

1. Seal migration is now completed. Take down the old active node, update its
   configuration of the old active node to use the new seal blocks (completely
   unaware of the old seal type) and bring it back up. It will be auto-unsealed if
   the new seal is one of the KMS seals, or will require unseal keys if the new
   seal is Shamir.

1. At this point, configuration files of all the nodes can be updated to only have the
   new seal information. Standby nodes can be restarted right away and the active
   node can be restarted upon a leadership change.

### Migration pre 1.5.1

#### Migration From Shamir to Auto Unseal

To migrate from Shamir keys to Auto Unseal, take your server cluster offline and
update the [seal configuration](/docs/configuration/seal) with the appropriate
seal configuration. Bring your server back up and leave the rest of the nodes
offline if using multi-server mode, then run the unseal process with the
`-migrate` flag and bring the rest of the cluster online.

All unseal commands must specify the `-migrate` flag. Once the required
threshold of unseal keys are entered, unseal keys will be migrated to recovery
keys.

`$ vault operator unseal -migrate`

#### Migration From Auto Unseal to Shamir

To migrate from Auto Unseal to Shamir keys, take your server cluster offline and
update the [seal configuration](/docs/configuration/seal) and add `disabled = "true"` to the seal block. This allows the migration to use this information to
decrypt the key but will not unseal Vault. When you bring your server back up,
run the unseal process with the `-migrate` flag and use the Recovery Keys to
perform the migration. All unseal commands must specify the `-migrate` flag.
Once the required threshold of recovery keys are entered, the recovery keys will
be migrated to be used as unseal keys.

#### Migration From Auto Unseal to Auto Unseal

~> **NOTE**: Migration between same Auto Unseal types is not currently
supported. We plan to support this officially in a future release.

To migrate from Auto Unseal to a different Auto Unseal configuration, take your
server cluster offline and update the existing [seal
configuration](/docs/configuration/seal) and add `disabled = "true"` to the seal
block. Then add another seal block to describe the new seal.

When you bring your server back up, run the unseal process with the `-migrate`
flag and use the Recovery Keys to perform the migration. All unseal commands
must specify the `-migrate` flag. Once the required threshold of recovery keys
are entered, the recovery keys will be kept and used as recovery keys in the new
seal.

#### Migration with Integrated Storage

Integrated Storage uses the Raft protocol underneath, which requires a quorum of
servers to be online before the cluster is functional. Therefore, bringing the
cluster back up one node at a time with the seal configuration updated, will not
work in this case. Follow the same steps for each kind of migration described
above with the exception that after the cluster is taken offline, update the
seal configurations of all the nodes appropriately and bring them all back up.
When the quorum of nodes are back up, Raft will elect a leader and the leader
node that will perform the migration. The migrated information will be replicated to
all other cluster peers and when the peers eventually become the leader,
migration will not happen again on the peer nodes.
